This invention relates to a push-pull cable motion transfer apparatus employing power assists means and particularly to power steering apparatus of such construction for outboard marine drive devices.
Remote transfer of a mechanical motion may be conveniently affected through known push-pull cable assemblies and such systems are widely employed in marine outboard drive systems for water craft, off-road vehicles and equipment and similar applications where a manual input is transmitted to a remote controlled device. For example, as shown in U.S. Pat. No. 3,136,283, a push-pull cable unit interconnects a steering wheel in the forward portion of a boat to a pendant outboard drive secured to the transom of the boat. The pendant outboard drive is mounted to pivot about a vertical axis for steering of the boat. The flexible push-pull cable unit extends between the steering wheel and a pivot arm connected to the pendent outboard drive. The cable unit employs an outer fixed casing or shaft fixedly secured at the opposite ends to the steering wheel support and to the dependent drive support. An inner core means generally a core wire is connected to the steering wheel and moves therewith. The opposite end of the core wire is secured to the pivot arm of the pendent drive.
The outer casing is formed of suitable flexible spring material and will assume a normal straight line condition unless positively curved while permitting guiding of the core about deliberate smooth bends formed in the mounting of the cable means. The casing and core are longitudinally rigid. The core, particularly when large load forces are encountered, is constructed with a high degree of longitudinal rigidity to prevent bending or jamming within the casing.
In many instances, a dual cable system may be employed with a pair of similar push-pull cable units coupled between the opposite sides of the steering mechanism extended along the opposite sides of the boat to the opposite sides of the pendent drive unit to provide a redundancy in the steering mechanism. If one system should fail, the second system maintains the necessary control. For example, in ocean racing, a pair of interconnected, outward drive units are normally employed and the craft may be traveling at speeds in the order of 80 miles per hour over relatively rough seas. It is absolutely essential, for any degree of safety, that steering be constantly maintained. Any significant loss of steering would, of course, result in an extremely dangerous situation.
Further, in applications such as ocean racing, as well as many instances of off-road equipment, relatively heavy steering loads are created. The operating personnel are therefore particularly subject to fatigue and power systems have been suggested and incorporated into the system. A particularly satisfactory power steering system employs a hydraulically activated power means coupled to the pendent drive unit. A pilot or servo valve is coupled to the push-pull cable unit. Generally, and particularly to the outer conduit or casing. The torque reaction on the conduit as a result of the steering and turning forces on the core is transmitted and actuates the servo valve, which, in turn, controls the power steering means.
The push-pull cable means is mounted between the steering means and the power means. As input forces are applied to one end of the core, the load at the opposite end opposes the applied force and creates a reaction force and torque on the casing which is employed to actuate the power means. In the dual steering systems, the core wires are coupled to the opposite sides of the single drive or the interconnected dual drive with a single power assist mounted to the one side of the unit and responsive to torque on the adjacent conduit.
While such power systems reduces the steering loads and minimizes the fatigue resulting from the more conventional push-pull systems, the power systems do not appear to significantly reduce the steering loads encountered in dual cable systems. Even, a single power system does not adequately relieve the fatigue characteristics which inherently includes backlash requiring continuous steering correction. The adjustment of a dual power steering system is quite critical and under operating conditions may ten to come out of adjustment, resulting in a possibly dangerous control situation. Applicant has also found that the dual power systems are not highly responsive under high or heavy load conditions. In particular, in ocean racing with wide open throttle and under heavy seas, the steering is quite non-responsive and demands a high degree of skill and large expenditures of energy on the part of the operating personnel.